There are many medicament delivery devices on the market that have been developed for self administration of medicament, where one large group is medicament injection devices. Many of these injection devices have been provided with removable needle cover assemblies where the core cover is a so called Rigid Needle Cover or Rigid Needle Shield (RNS).
These RNSs are arranged to protect the injection needle before use in order to keep the needle sterile and also protect from unintentional needle sticks. Many of these RNSs are pushed onto the neck portion of a medicament container, such as a syringe, where the RNS are provided with an inner cap in contact with the surface of the syringe. The inner cap is preferably of a resilient material, normally rubber that ensures a tight grip and a good seal between the cap and the syringe. However this tight grip entails a problem in that it is difficult to remove the RNS from the syringe in order to perform an injection.
Therefore a number of RNS removal devices have been developed, which are intended to aid the user in removing the RNS. International Publications WO2007/047200, WO 2006/106290, and WO 2005/115508 disclose different solutions to this problem. However, they all include a function where the whole assembly, including the RNS and its resilient inner cap, are twisted or rotated. This a major drawback since this twisting action of the inner cap very easily causes damage to the injection needles, which usually are thin and easily bendable such that when the RNS is removed, the needle has become so damaged it cannot be used for the injection.
International Publication WO 2009/01440 discloses an injection device comprising a cap including a central boss. A needle shield retainer provided with a shield grip and a shield pull component connected to the shield grip fits inside the central boss and can grip a needle shield tightly. Thus, as the cap is pulled off the housing, the needle shield is pulled away from the syringe with the cap. In addition, a first screw thread is provided on outside of the shield pull component which engages with a second screw thread provided on the inside of central boss.
Before injection, a user first rotates the cap many turns about the longitudinal axis away from the exit aperture. During rotation, the needle shield retainer does not rotate relative to a discharge nozzle and the rotational movement of the cap relative to the housing is converted into linear movement of the needle shield retainer away from the exit aperture in the axial direction achieved through engagement of the screw threads so the needle shield is pulled away from the discharge nozzle through the exit aperture into the central boss. After rotation, the user finally pulls the cap away from the housing, the needle shield and the discharge nozzle are not engaged with each other, and the cap becomes completely detached from the injection device.
The device according to WO 2009/01440 does not thus twist or rotate the needle shield but a rotational interaction with threaded components causes a linear movement of the needle shield retainer from the exit aperture of the medicament delivery device. The solution according to WO 2009/01440 does however include a number of components in order to obtain the aided linear movement of the needle cover assembly in order to remove the needle shield and is thus rather costly to manufacture. However, patients suffering from reduced hand dexterity experience difficulties in grasping and releasing the cap when it has to be rotated many turns.
There is thus a need for needle shield removal devices that provide the desired function without the risk of damaging injection needles and that at the same time are not so complex regarding use and manufacture.